Methods for treating and controlling medical, psychiatric or neurological disorders through the application of a modulated electrical signal to a selected nerve or nerve bundle in a patient are well known. Generally, the modulated signal is applied to the nerve or nerve bundle using a neurostimulator electrode assembly that is surgically implanted in the patient. Briefly, and in general terms, the neurostimulator electrode assembly comprises one or more electrodes positioned within a resilient circumneural carrier that is configured to be circumferentially positioned on the nerve. In order for the electrode to establish the requisite electrical contact with the nerve, the carrier must be able to securely hold the electrode against the nerve while not excessively circumferentially compressing the nerve. One example of a neurostimulator electrode assembly is shown and described in U.S. Pat. No. 6,600,956 B2 to Maschino, et al.
In order to accommodate nerves or nerve bundles of various diameters, neurostimulator electrode assemblies are available in standardized sizes that permit a surgeon to select the most appropriate size for implantation in a patient. Currently, the selection of the neurostimulator electrode assembly is made based upon a visual inspection of the nerve diameter. Selection of the electrode assembly by visual inspection has numerous drawbacks, however. If the surgeon selects an electrode assembly that has a diameter that is slightly too large, the electrodes within the assembly may fail to maintain adequate electrical contact with the nerve, as previously mentioned. If an electrode is selected that has a diameter that is too small, a nerve compression injury may result.
In order to overcome the shortcomings present in the visual estimation of a nerve diameter, the nerve diameter may be measured using conventional calipers of suitable size and resolution. Despite this obvious improvement, drawbacks nevertheless still exist. For example, a suitable measurement caliper may not be available to the surgeon while the implantation procedure is occurring. Even if a suitable caliper is available, conventional caliper devices generally possess relatively narrow tips that may cause the relatively compliant nerve to flatten during the measurement, thus rendering an inaccurate nerve diameter measurement.
Therefore, there is a need in the art for an accurate and inexpensive device to accurately measure a nerve diameter in order to achieve a consistent surgical outcome.